A U.S. military satellite detected a heat flash at the time a Russian jetliner crashed over the Sinai Peninsula last weekend, authorities said Tuesday, but the cause of the accident remains a mystery.

Authorities have ruled out the possibility that a missile hit the aircraft before it broke into pieces and plunged 9,400 meters to the Sinai desert, killing all 224 people aboard. Neither a missile launch nor engine burn has been detected.

But experts told U.S. media outlets that the heat flash could point to a catastrophic event aboard the aircraft, such as an exploding bomb, the explosion of an aircraft engine, or a fire aboard the Metrojet A-321, or even just the aircraft parts hitting the ground.

Egyptian President Abdel-Fattah el-Sissi on Tuesday dismissed as "propaganda" claims by Islamic State insurgents they brought down a Russian jetliner that crashed in the Sinai Peninsula, killing all 224 people aboard.

"When there is propaganda that it crashed because of ISIS, this is one way to damage the stability and security of Egypt and the image of Egypt," Sissi told the BBC, using an acronym for the Islamic State group.

"Believe me, the situation in Sinai, especially in this limited area, is under our full control," he said.

Meanwhile, investigators in Egypt began their examination of the flight recorders recovered from the wreckage of the Metrojet A-321 and Russian families began the sad process of identifying 140 bodies that were transported home to St. Petersburg.

Alexander Smirnov, the deputy general director of Metrojet, the Russian airline company speaks to the media about their plane, which crashed Saturday in Egypt's Sinai Peninsula, in Moscow, Russia, Nov. 2, 2015.

A Russian emergency official said 10 of the crash victims had been identified. In addition, more than 100 parts of bodies, personal belongings and documents have been recovered the desert crash site.

The plane went down Saturday over the Sinai about 20 minutes after takeoff from the airport at the Egyptian resort town of Sharm el-Sheikh on a flight to St. Petersburg. Three Ukrainians and a Belarussian were among the fatalities.

Cairo and Moscow have played down claims from Egypt's Islamic State branch that it downed the plane.

Aviation and military experts have voiced doubt extremists had missiles capable of hitting a target at an altitude of 9,400 meters.

'No direct evidence'

In Washington, U.S. Director of National Intelligence James Clapper said he knew of "no direct evidence" linking the crash to terrorism. He also said it was "unlikely" that Islamic State had the technical expertise to carry out such an attack, but said "I wouldn't rule it out."

White House spokesman Josh Earnest said U.S. investigators had offered to help probe the disaster. But he did not say whether that offer had been accepted by Moscow.

Russia's Ria Novosti news agency quoted Russian investigator Viktor Sorochenko as saying fragments of the Airbus A-321 were "strewn over a large area." He spoke after visiting the crash site.

A woman places flowers in front of the portraits of crew members of the crashed Airbus A321 plane, operated by Russian airline Kogalymavia, in the company's office in Moscow, Russia, Nov. 2, 2015.

Russian President Vladimir Putin said the crash was a tragedy.

"Without any doubt everything should be done so that an objective picture of what happened is created, so that we know what happened," Putin said.

Russia has sent about 100 experts to help Egyptian authorities search for the remains of victims and the aircraft debris.

Several airlines, including Air France, Lufthansa, Dubai-based Emirates and Qatar Airways, have said they will stop flying over the Sinai peninsula for safety reasons.

Egyptian Civil Aviation chief Hossam Kamal said safety checks before the flight did not turn up any problems, and he said the pilot did not issue a distress call before the plane disappeared.